docs: document defeq and type inference related functions - #12
Merged
Conversation
Reflow the docstrings added in the previous commit to the style used in the rest of the codebase: text starts on the `/--` line, `-/` closes the last line, and lines are wrapped at 100 columns (also applied to the new `--` comments, four of which ran to 100-187 columns). Incidental fixes while rewrapping: backtick and modernize the `cheapBetaReduce` example (Lean 3 `λ x, x` -> `fun x => x`, and the body is `xᵢ`, not `x₁`); `inferConstant` documents `.const name ls`, not `.const e ls`; `->` -> `→` and `cheapProj = true` -> `cheapProj := true`. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The docstrings added two commits ago were written against an older lean4lean and describe several things the code does not do. Rewritten against the current implementation: * `unfoldDefinitionCore` takes a `.const`, not an application with a constant head (that is `unfoldDefinition`); its doc had been copied from `isDelta`. * `isDelta` also requires the right number of universe levels, and the question of which constants delta-reduce is already settled by `ConstantInfo.deltaValue?`, so point at it rather than restating it. * `quickIsDefEq` defers constants and free variables too, not just applications and projections, and it refutes as well as confirms. Same correction in the `lazyDeltaReductionStep` and `lazyDeltaReduction` docs, which reused the wording. * `lazyDeltaReductionStep` hands `.unknown` back to `isDefEqCore'`, not `isDefEq`. * `reduceNat` was missing `Nat.succ`, `land`, `lor`, `xor`, `shiftLeft` and `shiftRight`, and `Nat.beq`/`Nat.ble` yield `Bool`, not `Nat`, literals. * `isDefEqOffset` decides `0 ≡ 0` before looking at successors. * `cheapBetaReduce` also reduces a body with no loose bvars, and leaves `e` alone in every other case, which is the point of the name. * `toCtorWhenStruct`'s `String` example predates `String` becoming a two-field structure over `ByteArray`; use `Prod`. Likewise `tryStringLitExpansionCore` matches `String.ofList`, which is no longer the constructor. * `inductiveReduceRec` applies the rule to the motives and minor premises as well as the parameters, accepts literal major premises, and re-applies the arguments past the major premise. * `inferType` also throws on resource exhaustion, so not "if and only if". * `isDefEqCore` referred to a `check` function; it is `checkType`. * `whnfFVar` uses `whnfCore`, and `whnfCore`'s `cheapRec` is never set. * `RecM.run` and `lazyDeltaReduction` take their limits from `FuelConfig`. All three `FIXME(kernel)` comments are rewritten as statements: each asked a question the code answers -- `cheapProj := true` leaves head projections unreduced, the recursive `whnfCore` call does reach `reduceRecursor`, and the eta-struct case is redundant work that the kernel performs identically -- so none of them is a divergence, and none stays a FIXME. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
digama0
added a commit
that referenced
this pull request
Aug 4, 2026
`whnfCore`'s `cheapRec` flag has never been set to `true` anywhere in this repo, so every `if cheapRec then ... else whnf e` took the `whnf` branch and the flag only cost us an argument to thread through eight functions. It is dead upstream too, so this does not diverge from kernel behavior. The flag was added in 2019 for one caller outside the kernel, `csimp`'s `is_stuck_at_cases`, which wanted to look through recursor applications without paying for delta-reduction. When lean4 commit 14260f454b split `cheap` into `cheap_rec`/`cheap_proj` so `is_def_eq` could use lazy projections alone, that caller moved to a new `whnf_core_cheap` wrapper; lean4#9275 then deleted the old compiler, and with it the only thing that ever passed `cheap_rec = true`. The wrapper survives in `type_checker.h` with no callers. Dropping it makes `reduceRecursor`'s `cheapProj` unused as well, since its sole use was inside the `cheapRec` branch, so that goes too. The `whnfCore` docstring added in #12 loses its `cheapRec` half, keeping a note that the kernel still carries the flag. The `Verify` proofs about these functions go through unchanged apart from the dropped argument, which is the check that behavior is unaffected. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Squash merge of PR #2 by rish987.
Reference: #2
Adds documentation for defeq and type-inference related functions to improve codebase understandability.